#ifndef MODEL_H
#define MODEL_H

#include <glad/glad.h> 

#include <glm/glm.hpp>
#include <glm/gtc/matrix_transform.hpp>
//#include <stb_image.h>
#include <assimp/Importer.hpp>
#include <assimp/scene.h>
#include <assimp/postprocess.h>

#include <mesh.h>
#include <shader.hpp>
#include <image.hpp>

#include <string>
#include <fstream>
#include <sstream>
#include <iostream>
#include <map>
#include <vector>
using namespace std;
namespace Engine{
    //unsigned int TextureFromFile(const char *path, const string &directory, bool gamma = false);

    class Model 
    {
    public:
        /*  Model Data */
        vector<Texture> textures_loaded;	// stores all the textures loaded so far, optimization to make sure textures aren't loaded more than once.
        vector<Mesh> meshes;
        string directory;
        bool gammaCorrection;

        /*  Functions   */
        // constructor, expects a filepath to a 3D model.
        Model(string const &path, bool gamma = false) : gammaCorrection(gamma)
        {
            loadModel(path);
        }

        // draws the model, and thus all its meshes
        void Draw(Shader & shader)
        {
            for(unsigned int i = 0; i < meshes.size(); i++)
                meshes[i].Draw(shader);
        }
        
    private:
        /*  Functions   */
        // loads a model with supported ASSIMP extensions from file and stores the resulting meshes in the meshes vector.
        void loadModel(string const &path)
        {
            // read file via ASSIMP
            Assimp::Importer importer;
            const aiScene* scene = importer.ReadFile(path, aiProcess_Triangulate  | aiProcess_CalcTangentSpace);//| aiProcess_FlipUVs
            // check for errors
            if(!scene || scene->mFlags & AI_SCENE_FLAGS_INCOMPLETE || !scene->mRootNode) // if is Not Zero
            {
                cout << "ERROR::ASSIMP:: " << importer.GetErrorString() << endl;
                return;
            }
            // retrieve the directory path of the filepath
            directory = path.substr(0, path.find_last_of('/'));

            // process ASSIMP's root node recursively
            processNode(scene->mRootNode, scene);
        }

        // processes a node in a recursive fashion. Processes each individual mesh located at the node and repeats this process on its children nodes (if any).
        void processNode(aiNode *node, const aiScene *scene)
        {
            // process each mesh located at the current node
            for(unsigned int i = 0; i < node->mNumMeshes; i++)
            {
                // the node object only contains indices to index the actual objects in the scene. 
                // the scene contains all the data, node is just to keep stuff organized (like relations between nodes).
                aiMesh* mesh = scene->mMeshes[node->mMeshes[i]];
                meshes.push_back(processMesh(mesh, scene));
            }
            // after we've processed all of the meshes (if any) we then recursively process each of the children nodes
            for(unsigned int i = 0; i < node->mNumChildren; i++)
            {
                processNode(node->mChildren[i], scene);
            }

        }

        Mesh processMesh(aiMesh *mesh, const aiScene *scene)
        {
            // data to fill
            vector<Vertex> vertices;
            vector<unsigned int> indices;
            vector<Texture> textures;

            // Walk through each of the mesh's vertices
            for(unsigned int i = 0; i < mesh->mNumVertices; i++)
            {
                Vertex vertex;
                glm::vec3 vector; // we declare a placeholder vector since assimp uses its own vector class that doesn't directly convert to glm's vec3 class so we transfer the data to this placeholder glm::vec3 first.
                // positions
                vector.x = mesh->mVertices[i].x;
                vector.y = mesh->mVertices[i].y;
                vector.z = mesh->mVertices[i].z;
                vertex.Position = vector;
                // normals
                vector.x = mesh->mNormals[i].x;
                vector.y = mesh->mNormals[i].y;
                vector.z = mesh->mNormals[i].z;
                vertex.Normal = vector;
                // texture coordinates
                if(mesh->mTextureCoords[0]) // does the mesh contain texture coordinates?
                {
                    glm::vec2 vec;
                    // a vertex can contain up to 8 different texture coordinates. We thus make the assumption that we won't 
                    // use models where a vertex can have multiple texture coordinates so we always take the first set (0).
                    vec.x = mesh->mTextureCoords[0][i].x; 
                    vec.y = mesh->mTextureCoords[0][i].y;
                    vertex.TexCoords = vec;
                }
                else
                    vertex.TexCoords = glm::vec2(0.0f, 0.0f);
                // tangent
                vector.x = mesh->mTangents[i].x;
                vector.y = mesh->mTangents[i].y;
                vector.z = mesh->mTangents[i].z;
                vertex.Tangent = vector;
                // bitangent
                vector.x = mesh->mBitangents[i].x;
                vector.y = mesh->mBitangents[i].y;
                vector.z = mesh->mBitangents[i].z;
                vertex.Bitangent = vector;
                vertices.push_back(vertex);
            }
            // now wak through each of the mesh's faces (a face is a mesh its triangle) and retrieve the corresponding vertex indices.
            for(unsigned int i = 0; i < mesh->mNumFaces; i++)
            {
                aiFace face = mesh->mFaces[i];
                // retrieve all indices of the face and store them in the indices vector
                for(unsigned int j = 0; j < face.mNumIndices; j++)
                    indices.push_back(face.mIndices[j]);
            }
            // process materials
            aiMaterial* material = scene->mMaterials[mesh->mMaterialIndex];    
            // we assume a convention for sampler names in the shaders. Each diffuse texture should be named
            // as 'texture_diffuseN' where N is a sequential number ranging from 1 to MAX_SAMPLER_NUMBER. 
            // Same applies to other texture as the following list summarizes:
            // diffuse: texture_diffuseN
            // specular: texture_specularN
            // normal: texture_normalN

            // 1. diffuse maps
            vector<Texture> diffuseMaps = loadMaterialTextures(material, aiTextureType_DIFFUSE, "texture_diffuse");
            textures.insert(textures.end(), diffuseMaps.begin(), diffuseMaps.end());
            // 2. specular maps
            vector<Texture> specularMaps = loadMaterialTextures(material, aiTextureType_SPECULAR, "texture_specular");
            textures.insert(textures.end(), specularMaps.begin(), specularMaps.end());
            // 3. normal maps
            std::vector<Texture> normalMaps = loadMaterialTextures(material, aiTextureType_HEIGHT, "texture_normal");
            textures.insert(textures.end(), normalMaps.begin(), normalMaps.end());
            // 4. height maps
            std::vector<Texture> heightMaps = loadMaterialTextures(material, aiTextureType_AMBIENT, "texture_height");
            textures.insert(textures.end(), heightMaps.begin(), heightMaps.end());
            
            // return a mesh object created from the extracted mesh data
            return Mesh(vertices, indices, textures);
        }

        // checks all material textures of a given type and loads the textures if they're not loaded yet.
        // the required info is returned as a Texture struct.
        vector<Texture> loadMaterialTextures(aiMaterial *mat, aiTextureType type, string typeName)
        {
            vector<Texture> textures;
            for(unsigned int i = 0; i < mat->GetTextureCount(type); i++)
            {
                aiString str;
                mat->GetTexture(type, i, &str);
                // check if texture was loaded before and if so, continue to next iteration: skip loading a new texture
                bool skip = false;
                for(unsigned int j = 0; j < textures_loaded.size(); j++)
                {
                    if(std::strcmp(textures_loaded[j].path.data(), str.C_Str()) == 0)
                    {
                        textures.push_back(textures_loaded[j]);
                        skip = true; // a texture with the same filepath has already been loaded, continue to next one. (optimization)
                        break;
                    }
                }
                if(!skip)
                {   // if texture hasn't been loaded already, load it
                    Texture texture;
                    //texture.id = TextureFromFile(str.C_Str(), this->directory);
                    Image img(str.C_Str());
                    texture.id = img.GetTBO();
                    texture.type = typeName;
                    texture.path = str.C_Str();
                    textures.push_back(texture);
                    textures_loaded.push_back(texture);  // store it as texture loaded for entire model, to ensure we won't unnecesery load duplicate textures.
                }
            }
            return textures;
        }
    };
}
#endif
